Unless otherwise indicated herein, the description in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations that radiate to define wireless coverage areas, such as sectors, in which user equipment devices (UEs), such as cellular phones, smartphones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
In general, a cellular wireless network may operate in accordance with a particular radio access technology or “air interface protocol,” with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and functions related to air interface communication.
In accordance with a recent version of LTE, the air interface on both the downlink and the uplink may span a particular bandwidth (such as 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, or 20 MHz) that is divided primarily into subcarriers that are spaced apart from each other by 15 kHz. Further, the air interface may be divided over time into a continuum of 10 millisecond frames, with each frame being further divided into ten 1 millisecond subframes or transmission time intervals (TTIs) that are in turn divided into two 0.5 millisecond segments. In each 0.5 millisecond time segment, the air interface may then be considered to define a number of 12-subcarrier wide “resource blocks” spanning the frequency bandwidth (i.e., as many as would fit in the given frequency bandwidth). In addition, each resource block may be divided over time into symbol segments of 67 μs each, with each symbol segment spanning the 12-subcarriers of the resource block and thus each supporting transmission of 12 orthogonal frequency division multiplex (OFDM) symbols in respective “resource elements.” Thus, a base station and a served UE may transmit symbols to each other in these resource elements, particularly on subcarriers that are spaced apart from each other by 15 kHz and in time segments spanning 67 μs each.
The LTE air interface may then define various channels made up of certain ones of these resource blocks and resource elements. For instance, on the downlink, certain resource elements across the bandwidth may be reserved to define a physical downlink control channel (PDCCH), and other resource elements may be reserved to define a physical downlink shared channel (PDSCH) that the base station can allocate on an as-needed basis to carry transmissions to particular UEs, with still other resource elements being reserved to define a downlink reference signal. Likewise, on the uplink, certain resource elements across the bandwidth may be reserved to define a physical uplink control channel (PUCCH), and other resource elements may be reserved to define a physical uplink shared channel (PUSCH) that the base station can allocate on an as-needed basis to carry transmissions from particular UEs.
During a communication session, a UE may engage in communication of bearer data (e.g., application layer communications, such as session initiation protocol (SIP) signaling, voice communication, video communication, file transfer, gaming communication, or the like), transmitting to the base station bearer data on uplink traffic channel resources (e.g., portions of a resource block of a PUSCH channel during a scheduled TTI) and receiving from the base station bearer data on downlink traffic channel resources (e.g., portions of a resource block of a PUSCH channel during a scheduled TTI). Typically, the UE and the base station transmit such bearer data in the form of data packets.
An effective data rate for bearer data sent between the network entity and the UE (e.g., the rate at which the UE and the network entity exchange data packets) depends at least in part on a wireless data rate for communications between the base station and the UE (e.g., the rate at which the UE and the base station wirelessly exchange data packets with each other). Generally speaking, the effective data rate varies with the wireless data rate; as the wireless data rate decreases, the effective data rate decreases. The wireless data rate in turn depends at least in part on several factors.
One such factor is air interface quality between the base station and the UE in the serving coverage area. On a given carrier, the wireless data rate may vary directly with air interface quality. By way of example, good downlink air interface quality between the base station and the UE in the serving coverage area (e.g., when the UE receives strong downlink channel signals) usually allows for a higher wireless data rate than poor downlink air interface quality (e.g., when the UE receives weak downlink channel signals). Further, when air interface quality between the base station and the UE in the serving coverage area is poor, the UE and/or the base station may receive incomplete data packets. This may require the UE or the base station to retransmit such data packets, thereby further reducing the effective data rate.
A second factor is the bandwidth of the carrier on which the UE receives service in the serving coverage area. Typically, a wider carrier bandwidth may support a higher wireless data rate. A 20 MHz carrier will usually allow for a higher data rate than a 5 MHz carrier for instance.
While the maximum bandwidth for a data transaction between a base station and a UE using a single carrier is 20 MHz (in an LTE system), it may be possible to increase the bandwidth for wireless communications with a UE beyond 20 MHz. A revision of LTE known as LTE-Advanced now permits a base station to serve a UE with “carrier aggregation,” by which a base station schedules bearer communication with the UE on multiple carriers at a time. With carrier aggregation, multiple carriers from either contiguous frequency bands or non-contiguous frequency bands can be aggregated to increase the bandwidth available to the UE. Using carrier aggregation, a base station may increase the maximum bandwidth to up to 100 MHz by aggregating up to five carriers. Each aggregated carrier is referred to as a “component carrier.” Further, when multiple carriers are aggregated, one of the component carriers may be defined as a primary cell (“PCell”) and the remaining component carriers may be defined as secondary cells (“SCells”). Further, a UE served with carrier aggregation may send and receive control signals and bearer data in the PCell and the SCells.